The trends of disease burden due to high temperature in Mainland China from 1990 to 2019 and its prediction to 2030

The risk of high-temperature-related diseases is increasing owing to global warming. This study aimed to assess the trend of disease burden caused by high temperatures in Mainland China from 1990 to 2019 and to predict the trend of disease burden over the next 10 years. The latest data were downloaded from the Global Burden of Disease Database (GBD) for analysis, and the disease burden related to high temperature was described by mortality and disability-adjusted life-years (DALYs) and stratified by etiology, sex, and age. Statistical analyses were performed using the R software. In 2019, there were 13,907 deaths attributed to high temperatures in Mainland China, and this was 29.55% higher than the 10,735 deaths in 1990. Overall, the age-standardized mortality and DALYs attributed to high temperatures showed a downward trend from 1990 to 2019. We observed an etiological shift in high-temperature-related diseases. The age-standardized DALYs contribution attributed to high temperatures in 1990 was mainly from communicable, maternal, neonatal, and nutritional diseases (CMNND) (21.81/100,000), followed by injury (18.30/100,000) and non-communicable diseases (10.40/100,000). In 2019, the largest contribution shifted to non-communicable diseases (10.07/100,000), followed by injuries (5.21/100,000), and CMNND (2.30/100,000). The disease burden attributed to high temperatures was higher in males than in females and increased with age. In 2030, the mortality rate and DALYs due to high temperatures are predicted to decrease further, and the largest contribution will come from chronic non-communicable diseases, the occurrence of which will remain at a high level over the next 10 years. The burden of disease due to high temperatures in Mainland China is still heavy, mainly due to population aging and an increase in non-communicable diseases.


Definition
Age standardized rate (ASR) The age-standardized rate (ASR) was used to estimate trends.The calculation of the ASR is based on the age structure of a certain population, which can reflect the constantly changing population composition patterns.In this study, the disease burden due to high temperatures was represented by the ASR of deaths and the ASR of DALYs.

Disability adjusted life years (DALYs)
DALYs refer to comprehensive indicators for calculating the sum of years of life lost and years of life lived with a disability and are widely used in disease burden research.

Estimated annual percentage change (EAPC)
The estimated annual percent change (EAPC) can be used as an indicator to evaluate the average annual percentage change in ASR over the selected period.The calculation formula is as follows: EAPC = 100 × (exp (exp(β) − 1) 16 .β is the regression coefficient in a linear regression model.If both EAPC and 95% CI did not contain 0, the disease showed an increasing or decreasing trend; otherwise, the disease showed a stable trend.

Prediction analysis
For the prediction of high temperatures burden, Nordpred model was used.Nordpred model was shown to have a relatively lower error rate before 17 .The average trend based on all observed data was extrapolated out to the year 2030 18 .Firstly, download the 1990-2019 demographic data and high-temperature related ASR from the GBD 2019 database, and read the predicted demographic data in the database (https:// ghdx.healt hdata.org/ data-type/ estim ate).Subsequently, the R package Nordpred was used to predict the trend of burden due to high temperatures in the future.

Statistical analysis
The data on death, DALYs, ASR, and 95% uncertainty interval (UI) due to high temperatures were collected.R software was used to extract and analyze the data.Trends in disease burden due to high temperatures were plotted using R software, and the sample was stratified by sex and age.The R package Nordpred was used to predict the trend in disease burden due to high temperatures over the next 10 years.

Disease burden due to high temperature
The trends in the disease burden due to high temperatures in Mainland China are shown in Table 1.The deaths due to high temperatures increased by 29.55% between 1990 and 2019, from 10,735 cases to 13,907 cases.Death cases due to high temperatures showed a wave-like increasing tendency every year from 1990 to 2019 in Mainland China (Fig. 1A).The ASR of deaths showed a downward trend from 1990 (1.39/100,000) to 2019 (0.9/100,000),

Stratified analysis by gender and age
In 2019, the number and ASR of deaths were 7850 and 1.23/100,000 for males, respectively, which were far higher than those for females (6057 and 0.69/100,000, respectively).From 1990 to 2019, the ASR of deaths due to high temperatures in males showed a stable trend (95% CI of EAPC including 0), while in females it showed a decreasing trend (both EAPC and 95% CI were less than 0).In 2019, the DALYs and ASR of DALYs were 174,213 and 23.73/100,000 for males, respectively, which were significantly higher than those for females (101,919 and 12.19/100,000), respectively.From 1990 to 2019, the ASR of DALYs for both males and females showed a downward trend (Fig. 2A-D for details).The disease burden due to high temperatures varied significantly among the different age groups, as shown in Fig. 3A-D.The highest number of deaths in 2019 was in the ≥ 70 year-old-group (9814 cases), followed by those aged 50-69 (2794 cases) and 25-49 (845 cases).Overall, the number of deaths increases with age.The ASR of deaths also showed the same trend, with the highest in the ≥ 70 age group (9.09/100,000), followed by those aged 50-69 (0.76/100,000) and 25-49 (0.15/100,000).After further analysis of the trends in ASR of deaths among different age groups, it was found that the ≥ 70 year-old group showed a stable trend from 1990 to 2019 (95% CI of EAPC including 0), while other age groups showed a decreasing trend (EAPC < 0).In 2019, the heaviest burden

Prediction analysis
Table 2 predicts the disease burden due to high temperatures in Mainland China from 2020 to 2030 using the R software.The predicted ASR of deaths due to high temperatures in 2030 is 0.82/100,000, with 1.13/100,000 for males and 0.57/100,000 for females.The highest contribution to the ASR of deaths due to high temperatures came from non-communicable diseases (0.61/100,000), followed by CMNND (0.11/100,000) and injuries (0.07/100,000).As shown in Fig. 4A-D, the predicted trend of the ASR of deaths due to high temperatures from 2020 to 2030 showed a significant decrease in CMNND and injuries, while the ASR of deaths due to overall cause and non-communicable diseases remained relatively stable.The predicted ASR of DALYs attributed to high temperatures in 2030 is 15.05/100,000, with 20.92/100,000 for males and 9.69/100,000 for females.Similarly, the largest contributing ASR of DALYs due to high temperatures comes from non-communicable diseases (9.02/100,000), followed by injuries (3.63/100,000) and CMNND (2.18/100,000).As shown in Fig. 5A-D, the predicted ASR of DALYs due to high temperatures from 2020 to 2030 among the overall cases, as well as CMNND and injuries, showed an overall decreasing trend, while the non-communicable disease group showed a stable trend.

Discussion
This study analyzes the trends of disease burden due to high temperatures in Mainland China from 1990 to 2019 using data from GBD 2019 and makes a prediction for the next 10 years.These results suggest that the disease burden due to high temperatures in Mainland China remains heavy.The number of deaths showed a further upward trend, but it is gratifying that the ASR of deaths and DALYs showed a downward trend.In addition, the etiology due to high temperatures changed between 1990 and 2019, with the main contribution coming from CMNND in 1990 and transitioning to non-communicable diseases in 2019.The ASR of deaths and DALYs due to high temperatures in males were higher than those in females, while the ASR of deaths and DALYs due to high temperatures increased with age.Predictive analysis showed that the ASR of deaths and DALYs due to high temperatures will continue to decline from 2020 to 2030, whereas that of non-communicable diseases due to high temperatures will remain stable for the next 10 years.This study provides a comprehensive understanding of the impact of high temperatures on health under global warming trends, which will be helpful for formulating public health policies.The disease burden due to high temperatures in Mainland China shows significant fluctuations, which are related to the temperature fluctuations in China 19 .A study by Li et al. showed that the national average temperature showed a significant upward trend from 1964 to 2008 20 .Lan et al. analyzed data from 118 meteorological stations in China from 1969 to 2018 and showed a significant trend of warming in all seasons, with rates of increase in spring, summer, autumn, and winter at 0.347, 0.125, 0.200, and 0.302 °C/10a, respectively 21 .This finding can be attributed to changes in work patterns.With the continuous advancement of industrialization and urbanization, manual labor, which must withstand high temperatures, is gradually being replaced with machines and industrial automation.For example, traditional manual labor, such as farming, steelmaking, and mining, has begun to be mechanically automated, whereas positions such as technical personnel, administrative personnel, financial practitioners, and sales personnel are currently increasing and are mainly concentrated in office environments 22 .In addition, improvements in hygiene conditions are also an important reason for the decreased burden due to high temperatures.In the past, poor hygiene conditions in China led to an outbreak of infectious diseases in a large population, seriously threatening human life and health.With continuous progress in medical technology and significant improvements in living conditions, the incidence rates have gradually declined and cure rates have greatly improved of many infectious diseases 23 .However, with the increasing use of air conditioning in offices owing to global warming, carbon emissions have greatly increased, accelerating the progress of global warming and creating a vicious cycle where humans will have nowhere to hide, which requires the attention and participation of all humanity.
The ASR of deaths and DALYs caused by non-communicable diseases due to high temperatures is still relatively high, and we should attach great importance to them.
There is a certain relationship between global warming and the increase in non-communicable diseases 24 .Firstly, global warming has exacerbated the problem of air pollution, especially particulate matter and ozone in the atmosphere.These pollutants are closely related to the risk of non-communicable diseases such as heart disease, stroke, respiratory diseases, and cancer 25 .Secondly, global warming exacerbates extreme weather events such as heatwaves, droughts, floods, and hurricanes.These weather events can lead to heat stress, dehydration, insufficient food and water supply, thereby increasing the risk of diseases such as heart disease, respiratory system disease, kidney disease, and stroke 26,27 .Finally, global warming has a complex impact mechanism on the increase of non-communicable diseases.Therefore, comprehensive measures need to be taken to address climate change, including reducing greenhouse gas emissions, improving air quality, improving health education, and responding to extreme weather events 28,29 .These measures help reduce the risk of non-communicable diseases and promote human health and well-being.
The ASR of deaths and DALYs due to high temperatures in males were higher than those in females.There are indeed studies indicating gender differences in high-temperature tolerance 30 , but the specifics have not yet been determined.Some studies suggest that there are differences in physiological structure and function between males and females.For example, men usually have larger bodies than women, relatively smaller surface area, and weaker heat dissipation ability 31 .In certain cultural and social environments, men may be more inclined to exhibit adventurous and courageous behavior, leading to them not paying attention to health risks in hightemperature environments.On the contrary, women may be more inclined to adopt conservative behavior and prioritize health and safety 32 .
The aging population is another reason for the rising number of deaths due to high temperatures, and our study also confirms that the disease burden due to high temperatures is directly proportional to age, which is consistent with other research results 33    1.5 times 35 .Therefore, with the deepening of misconduct in the aging population, it is of great significance to formulate relevant policies to reduce high-temperature exposure in the elderly and help them improve their self-protection and prevention awareness.This study had certain limitations.First, the scope of this study mainly covered very large countries.Owing to the large land area of China and significant temperature changes in various regions, the large number of research units may cause difficulties in the implementation of specific health policies.Second, the data of this study were from the GBD database in 2019, and the indicators related to the burden of disease were converted from different models; thus, there is a high requirement for the authenticity of the data.Although GBD uses standardized tools and processes to improve the accuracy and robustness of data, there are still differences and biases in the data transmission process.

Conclusions
In summary, this study revealed the disease burden caused by high temperatures in Mainland China from 1990 to 2019 and predicted the burden from 2020 to 2030.The results indicate that the disease burden due to high temperatures in Mainland China is still relatively heavy and is mainly related to population aging and an increase in non-communicable diseases.

Figure 1 .
Figure 1.Trend of disease burden due to high temperatures from 1990 to 2019.(A) Number of deaths; (B) ASR of deaths; (C) number of DALYs; (D) ASR of DALYs.

Figure 2 .
Figure 2. Trend of disease burden due to high temperatures from 1990 to 2019 grouped by gender.(A) Number of deaths; (B) ASR of deaths; (C) number of DALYs; (D) ASR of DALYs.
. The aging population in China has been accelerating since 1990, and by 2020, the population aged 65 years and above has reached 190 million 34 .Research by Yang et al. showed that the aging population increased the number of deaths due to high temperature by 2.3-5.8times.Data from South

Figure 3 .
Figure 3. Trend of disease burden due to high temperatures from 1990 to 2019 grouped by age.(A) Number of deaths; (B) ASR of deaths; (C) number of DALYs; (D) ASR of DALYs.

Table 1 .
Trend of disease burden due to high temperature in Mainland China from 1990 to 2019.CMNND communicable, maternal, neonatal, and nutritional diseases.

Table 2 .
Korea also show that the mortality rate related to high temperatures in South Korea increased by 4-6 times from 1992 to 2010.After removing the impact of population aging, the mortality rate only increased by 0.5 to Prediction of disease burden due to high temperature in Chinese Mainland from 2020 to 2030.CMNND communicable, maternal, neonatal, and nutritional diseases.